With the advent of power operated vehicle accessories, such as power lift gates, power sliding doors, power deck lids, power swing doors, power sunroofs, etc., comes a need for position sensors capable of tracking the position of moving components. Sensing the position of these moving components is often necessary for accomplishing other tasks, for instance, controlling the speed at which the component is driven relative to its current position, calculating the amount of time between known positions to determine if the moving component has encountered an obstacle, etc. Various techniques have been employed for monitoring the position of moving components, one of which involves sensing the position of a component other than the actual power accessory, knowing the relationship between that separate component and the power operated accessory, and calculating the relative position of the power operated accessory based upon this relationship. For example, U.S. Pat. No. 5,979,114 issued Nov. 9, 1999 to Clark et al. discloses a power sliding door for use with a vehicle that includes a relative position sensing system for determining the position of the sliding door. This system includes position sensing means coupled to a clutch, wherein the sensing means produce an electronic signal indicative of the rotary position of the clutch which, in turn, is sent to an electronic control unit (ECU). Because the clutch is mechanically coupled to the drive mechanism which moves the sliding door, the ECU is capable of determining the relative position of the sliding door based upon the rotational position of the clutch. Accordingly, the relative position sensing system of the Clark patent does not measure the actual position of the sliding door, rather, it measures the rotational position of another component, the clutch, and the ECU utilizes that reading to calculate the relative position of the sliding door. Though relative position sensing systems, such as that just described, have been useful in the past, these techniques remain susceptible to certain drawbacks. For instance, if a relative position sensing system were to experience an unforeseeable power outage and the position data of the related component were lost, upon power restoration, the system would likely be unable to calculate the position of the power accessory without executing some type of recalibration sequence. Also, relative position sensing systems typically require significant tweaking before the system is capable of operating the power accessory in a precise, smooth manner. Accordingly, there exists a need for an absolute position sensing system that directly determines the position of the power-operated accessory.
Furthermore, there exists a need for a position sensor capable of tracking the position of a power operated vehicle accessory operating in either a power or a manual mode. Many power-operated accessories are now capable of being driven in either power or manual modes, a feature that gives the operator the ability to use whichever mode is most convenient. For instance, the power sliding door disclosed in the Clark patent is capable of both manual and power operation, therefore if the sliding door is being closed under the force of the power drive unit and an operator were to manually engage the door, they would be able to overtake operation of the door and complete the closing process manually. Thus, it is desirable that a position sensor coupled to a dual power/manual operated vehicle accessory, be able to track the position of the moving accessory component regardless of its mode of operation.
Moreover, there exists a need for providing a position sensor having a low power consumption feature, particularly if the vehicle accessory is capable of being manually operated. In the manual mode, the vehicle accessory can be left in a partially open position for an indefinite amount of time, thereby potentially causing significant power consumption if the electronic position sensor were to be provided with a normal amount of power. Therefore, electronic position sensors capable of low power consumption are advantageous, particularly when they are used in conjunction with power operated vehicle accessories that can also be manually operated.
Thus, it would be advantageous to provide an electronic position sensor for use with a power operated vehicle accessory, wherein the sensor is capable of tracking the absolute position of the accessory in either a power or a manual mode, and the sensor is further capable of being selectively operated in a low power consumption mode.